This invention relates generally to the field of transportable cooling units comprising a relatively large compartment for receiving produce such as fruits and vegetables and means to rapidly reduce the temperature of the produce within the compartment for subsequent transfer into delivery trailers. More particularly, the invention relates to units which incorporate the techniques of hydro cooling, where chilled water is directed over and through the produce, and forced refrigerated air cooling, where air is cooled by a refrigerant expansion system and circulated through the produce.
When fruits and vegetables are harvested, the ripening or spoilage process begins immediately. It is well known that cooling or refrigeration of the produce slows ripening and reduces this deterioration, thus increasing shelf life and freshness. The more rapidly the produce is cooled following harvest, the better the results. Since harvesting usually occurs during warm weather months, the produce contains a large amount of field heat. Additionally, the produce itself creates heat through respiration. The deterioration due to heat is directly related to loss of moisture from the produce, which shortens shelf life and reduces the quality of the produce. The differential in vapor pressure between the produce cells and the surrounding air determines the rate of moisture loss. Low air temperature and high moisture content lowers moisture loss from the produce. For certain produce rapid cooling by hydro cooling is preferred, for other types of produce cooling by refrigerated air is preferred, and for others a combination of the two may be best. Alternatively, environmental or other site specific conditions may dictate the preferred cooling method.
Since it is most beneficial to cool the harvest as soon as it is picked, transportable cooling units have been developed to provide means to accomplish the cooling at the harvest site itself, the provision of permanent cooling structures at the vast number of harvest sites being cost prohibited and not optimally effective since construction of a permanent cooling structure at a generally centralized location requires the produce to be first transported to the structure, with heat deterioration occurring during the transport and waiting period. One approach to cooling the produce immediately upon harvest at the harvest site has been to improve the cooling efficiency of the refrigerated produce delivery trailers themselves, i.e., the trailers used to transport the harvest from the field to the distribution or processing centers, such that less time is required to reach the desired temperature once the delivery trailers are loaded. The problem with this approach is that a compromise must be maintained between the desire to lessen the weight and space requirements of the cooling equipment, so that container space and fuel efficiency is maximized, and the desire to maximize the efficiency of the cooling equipment, since reducing the time required to cool the produce is directly related to the weight, size and type of the equipment utilized. Thus while advances have been made in improving the cooling efficiency of the delivery trailers, the more optimum approach has been directed toward providing specialized portable cooling units with large and efficient cooling capabilities which can be driven to the individual harvest sites, where the portable cooling units are used to rapidly cool the produce prior to loading into the delivery trailers or to cool the delivery trailers after the produce has been loaded, the increased cooling capability of the large portable cooling units providing a relatively rapid reduction in temperature not attainable by the limited cooling units incorporated into the delivery trailers.
There are several common methods utilized to cool the produce after harvest. The most common method is by the use of a recirculating refrigerant unit which circulates a refrigerant gas such as Freon through an expansion/compression cycle with warm air, either external air from the ambient or preferably air within the trailer, being drawn across cooling coils to reduce the temperature of the air. The cooled air is then passed through the produce by forced air means such as a fan. Another method is known as cryogenic cooling, where a reserve of super-cooled gas such as liquid nitrogen or carbon dioxide is allowed to expand by spraying it into the trailer, causing heat to be drawn from the produce. Still another method is known as hydro cooling, where chilled water is sprayed onto the produce from overhead nozzles, the water being drained or recycled, as shown in U.S. Pat. No. 3,961,925 to Rhoad.
It is known to provide several of the known cooling methods into a single portable cooling unit. For example, U.S. Pat. No. 4,060,400 to Williams and U.S. Pat. No. 4,936,100 to Leppa show a trailer which encompasses both a cryogenic cooling unit and a mechanical refrigeration cooling unit. U.S. Pat. No. 4,406,131 to Weasel, Jr., teaches a trailer utilizing both hydro cooling and cryogenic cooling. U.S. Pat. No. 3,604,217 to Spear shows a combination hydro cooling and vacuum cooling unit.
A drawback to cryogenic systems where the trailer is filled with a nitrogen, carbon dioxide or other non-breathable gas is that the units must be purged and the atmosphere replaced with ambient air before personnel can enter the trailer. In addition, the cryogenic gases must be transported to the remote harvest sites, since on-site sources will not be available.
It is therefore an object of this invention to provide a portable apparatus and method for the rapid cooling of produce at the harvest location, where the produce is placed into the portable cooling apparatus, cooled sufficiently and then transferred into delivery trailers for removal from the harvest site, where the cooling methodology involves the use of forced air refrigeration, hydro cooling or both, and where the forced air refrigeration equipment involves passing air through a chilled water cascade in a heat exchanger with the cooled air then forced through the produce and circulated back through the water cascade, and further where the cooling unit can be utilized as a hydro cooler by importing additional water from an on-site water source, chilling the water in the water cascade, pumping the cooled water onto the produce through nozzles in the ceiling of the trailer and recapturing the water in a capture reservoir under the trailer floor to cycle it back through the heat exchanger for recooling.